Estrogen is a generic term for estrus-producing steroid compounds. Within the "estrogen group" are the traditional steroids such as 17b-estradiol and estrone (the major estrogens in humans), as well as various metabolites such as the estratriols, sulfates and glucuronides of estradiol and estrone. Also, germane to human medicine, are the steroidal equine estrogens such as the equilins, in that they are administered to humans in preparations, such as Premarin.TM..
Also, certain compounds known as "anti-estrogens", e.g., tamoxifen, clomiphene, nafoxidene, and raloxifene, demonstrate varying degrees of estrogen agonist properties in some tissues; however they act to antagonize the natural estrogens and their function in other tissues.
Recently, these "anti-estrogens" have been categorized into three different types depending on their degree and mix of estrogen agonist/antagonist properties which is based on their ability to freeze estrogen receptors in different conformational states, cf. D. P. McDonnell, et al., Molecular Endocrinology, 9(6): 659-669 (1995). Most germane to the present invention are the so-called "type II anti-estrogens" of which compounds of the current invention belong. The chemical structures of these various anti-estrogen types, although often similar, are poor predictors of pharmacological activity, in that small chemical changes produce varied activity.
Estrogens as biologically active molecules exert their properties by binding to an intracellular receptor. After the receptor and bound ligand are transported to the nucleus of a cell, the complex exerts its effect by binding to certain recognition sites on DNA and allowing certain genes to be expressed. This binding to the receptor and regulation is poorly understood; however, it appears to be crucial to the varying agonist and antagonist properties of the anti-estrogens. Thus, certain types of anti-estrogens allow agonist activity in some tissues, but are antagonists in others. Hence, the term, "selective estrogen receptor modulators" (SERMs) has been proposed to describe these molecules, especially the type II, of which the compounds of the current invention are members.
Estrogen has long been classified as "the female sex hormone" and a great deal of literature describes its activity as such. However, in recent years, research has shown that estrogens have many other homeostatic functions, other than those related to female reproduction and the functioning of sex tissues. Indeed, it has been shown that males possess estrogen receptors and DNA recognition sites and possess the ability to produce estrogens in many tissues, such as those involved in the cardiovascular system. The exact nature of the effects of estrogens in both men and women, outside the productive aspects, are only beginning to be explored and are currently poorly understood.
The majority of the documented activities of the estrogens have been derived from studies in women, since most women suffer from the most obvious effects of estrogen, mainly due to menopause and estrogen dependent cancers. The clinical pathologies associated with estrogen levels and their subsequent function, can be categorized into two main types, i.e., those which are due to a deprivation or lack of estrogen and those which are due to an aberrant physiological response to existing estrogen in estrogen sensitive tissues. SERMS, especially those of the current invention, have the property of being estrogen agonists in those cases where estrogen deprivation is a cause of pathology (mainly in non-sex related tissues) and simultaneously being antagonists of the pathologies caused by abnormal responses to endogenous estrogen (in sex related tissues).
Thus, SERMS of the type II class have the potential to effectively treat a variety of estrogen dependent pathological conditions.